Group III nitrides such as GaN have superior semiconductor properties and are therefore used as materials suitable for semiconductor devices.
For example, Japanese Patent Laying-Open No. 2009-126722 (PTD 1) discloses a free-standing group III nitride substrate to be used as a substrate for a semiconductor device. The free-standing group III nitride substrate has a diameter of 25 mm or more and 160 mm or less and a thickness of 100 μm or more and 1000 μm or less. It discloses, as a specific example thereof a free-standing GaN substrate having a diameter of 100 mm and a thickness of 400 μm.
Japanese Patent Laying-Open No. 2008-010766 (PTD 2) discloses a GaN-thin-film-bonded substrate to be used as a substrate for manufacturing a semiconductor device. The GaN-thin-film-bonded substrate includes a heterogeneous substrate whose chemical composition is different from that of GaN, and a GaN thin film having a thickness of 0.1 μm or more and 100 μm or less and bonded to the heterogeneous substrate. It discloses, as a specific example thereof, a GaN-thin-film-bonded substrate having a diameter of 50.8 mm and including a sapphire substrate and a GaN thin film having a thickness of 0.1 μm or 100 μm and bonded to the sapphire substrate.
Japanese Patent Laying-Open No. 2010-182936 (PTD 3) discloses a composite substrate to be used as a substrate for a semiconductor device. The composite substrate includes a support substrate, a nitride semiconductor layer, and a joint layer disposed between the support substrate and the nitride semiconductor layer. It discloses, as a specific example thereof, a composite substrate having a diameter of 50.8 mm and including a sapphire substrate, a GaN layer, and a joint layer formed by press fitting between the substrate and the GaN layer, in which the GaN layer has a thickness of 5 μm to 220 μm.